Cardiac Arrest, or Sudden Death, is a descriptor for a diverse collection of physiological abnormalities with a common cardiac etiology, wherein the patient typically presents with the symptoms of pulselessness, apnoea, and unconsciousness. Cardiac arrest is widespread, with an estimated 300,000 victims annually in the U.S. alone and a similar estimate of additional victims worldwide. Sudden cardiac arrest is a leading cause of death in the United States, with a greater public health impact in measures of mortality than cancer, HIV, stroke or infectious diseases. Approximately 40-50% of cardiac arrest victims are resuscitated by paramedics and emergency medical technicians (EMTs) in the field and brought to the hospital for further treatment; however, due to the insult on the victim's vital organs from the cardiac arrest, typically only about 25% (or approximately 40,000 out of 600,000 cardiac arrest victims, worldwide) of those victims who survive to the hospital will survive to being discharged from the hospital.
The treatment window for cardiac arrest with current treatments of defibrillation, cardiopulmonary resuscitation, and inotropic (e.g., epinephrine) drug treatment is very narrow. Long term survival rates from the time of victim collapse decrease at a roughly exponential rate with a time constant of roughly 2 minutes. Thus, just two minutes of delay in treatment using the currently recommended treatment protocols result in a long term survival rate of 30-35%. After 15 minutes, the long term survival rates are below 5%.
During cardiac arrest, cerebral blood flow ceases and global cerebral hypoxic-ischemic injury begins within minutes. Myocardial and neuronal tissue is able to remain viable during prolonged periods of ischemia (as long as twenty minutes), but paradoxically will sustain immediate damage during the return of circulation and oxygenation. It has been shown in a variety of studies at the tissue-level and animal model that successful resuscitation with return of spontaneous circulation (ROSC) leads to a secondary cascade of injury related to reperfusion injury. This reperfusion injury is particularly acute in neuronal tissue.
After successful cardiac resuscitation and ROSC, cerebral blood flow may remain abnormally low for several hours. After an initial hyperemia resulting from high circulating levels of catecholamines, cerebral blood flow decreases just as the cerebral metabolic rate for oxygen increases. This can lead to a prolonged state of relative cerebral ischemia. This prolonged mismatch between cerebral metabolic rate and blood flow, and ongoing biochemical and molecular processes related to delayed neuronal apoptotic and necrotic cell death, provide the scientific rationale for induced hypothermia as a form of neuroprotection after cardiac arrest. One method developed is the cooling of comatose cardiac arrest survivors to approximately 34° C. within 4 hours of arrest onset, which has been shown in several studies to enhance the survival rates of patients who are initially resuscitated (the approximately 40-50% of victims making it to the hospital). Hypothermia is common in the cardiac intensive care, hospital environment such as in bypass operations, etc, but there are two related drawbacks of hypothermia which have prevented its widespread use in the pre-hospital environment.
The first of these drawbacks is the primary biomedical engineering challenge of hypothermia: the large thermal mass of the victim and the difficulty of cooling the victim quickly and safely. While it has been shown that hypothermia is beneficial as long as it is applied within 4 hours of cardiac arrest, studies have also shown that cooling prior to resuscitation provides additive therapeutic benefits. While the causes for this are only speculative, one of the factors is likely the positive effects of hypothermia during the reperfusion phase of resuscitation. Practically speaking, it is highly undesirable to delay defibrillation and resuscitation to cool a patient to the proper temperature. Non-invasive methods of cooling take at minimum 10 minutes to 1 hour, while invasive methods such as extraction and cooling of the blood may take only 3-5 minutes, but are hazardous to the patient, particularly in the pre-hospital environment. In the case of defibrillation, even a delay of 3 minutes can result in a decrease in survival of 30%. While hypothermia may be effective at counteracting longer-term deleterious effects of ischemia and reperfusion, it would be desirable to have a treatment that can provide immediate protective effects against reperfusion injury while, at the same time, not delaying any current resuscitation interventions.
The phosphatidylinositol-3 kinase (PI3K)/protein kinase B (PKB or Akt) pathway is pivotal for cellular homeostasis, neurological development, metabolism, and other processes. It regulates various aspects of cellular development such as apoptosis, cell cycle progression, and cell differentiation. The lipid phosphatase and tensin homolog (PTEN), which dephosphorylates PIP3 to PIP2, has been shown to limit Akt activation by decreasing PIP3. Deletion or mutation of PTEN is observed in many types of tumors and is accompanied by high Akt activity. Further, protein kinase N2 (PKN2), also known as protein kinase C-related kinase-2 (PRK2), may negatively regulate Akt by inhibiting phosphoinositide-dependent kinase 1 (PDK1) activation of Akt. The kinase domain of PDK1 interacts with a region of PRK2 encompassing the PDK1-interacting fragment (PIF) including the hydrophobic motif FXXFDY (SEQ ID NO:207) (Balendran, et al. (1999) Curr. Biol. 9:393-404). Moreover, protein phosphatase (PP)2A is known to dephosphorylate Akt at Thr308 and/or Ser473 in noncardiac cells. A pharmacological study also suggests that in retina PP2B (calcineurin) can dephosphorylate Akt at both sites. A more specific Akt-directed PP2C family member protein phosphatase, PHLPP (pleckstrin homology (PH) domain leucine-rich repeat protein phosphatase), has been identified. Two isoforms of PHLPP, PHLPP-1 and PHLPP-2, have been shown to selectively dephosphorylate the hydrophobic motif of Akt (Ser473) via the PDZ binding motif (Gao, et al. (2005) Mol. Cell 18:13-24) thereby terminating Akt signaling. PHLPP levels are markedly reduced in several cancer cell lines, resulting in elevated Akt activation. Conversely heterologous expression of PHLPP in cancer cells can prevent Akt activation and promote apoptotic death. In this respect, the administration of PHLPP has been suggested for use in the treatment of cancer (US 2008/0108569).
In cardiac myocytes, overexpression of PTEN has been shown to be proapoptotic, whereas genetic deletion of PTEN rescues hearts from ischemia/reperfusion (I/R) injury (Schwartzbauer & Robbins (2001) J. Biol. Chem. 276:35786-93; Ruan, et al. (2009) J. Mol. Cell Cardiol. 46:193-200). Similarly, PHLPP-1 knockdown via siRNA or knockout in cardiomyocytes potentiates Akt phosphorylation at 5473 induced by agonists (Miyamoto, et al. (2010) Circ. Res. 107:476-84).
In support of a role for PTEN in I/R injury and protection, it has been demonstrated that VO-OHpic (VO), a vanadyl small molecule compound that demonstrates potent inhibition of PTEN, induces cooling-like cardioprotection with an almost four-fold reduction in cell death and significant increase of phosphorylated Akt (Zhu, et al. (2014) PLoS One 9:e95622), as well as improved recovery and survival in an established mouse model of SCA (Li, et al. (2015) Am. J. Physiol. Heart Circ. Physiol. 308:H1414-22). Similarly, the use of insulin has been suggested to decrease PHLPP-1 protein levels, activate Akt phosphorylation, promote myocardial cell survival, and afford protection of the ischemic heart (CN 201210382244).
Peptides DQHSQITKV (SEQ ID NO:4) and DQHTQITKV (SEQ ID NO:5), based on the PDZ domains of rat and human PTEN proteins, respectively, have been described for use in treating a retinal degenerative disorder or stroke (US 2014/0371161). Peptide LPDYYDTPL (SEQ ID NO:9), based upon the PDZ domain sequence of human PHLPP-1, has been shown to be useful in the production of anti-PHLPP1 antibodies (Jackson, et al. (April 2015) Sci. Rep. 5:9377). Further, peptides having the sequence REPRILSEEEQEMFRDFDYIADWC (SEQ ID NO:208) have been suggested for use in treating cancer, stroke and myocardial infarction (US 2007/0196883).